For the first time in the historical record, accumulated cyclone energy (ACE) index was above normal for a 6-year period (2016-21) averaging 159 which is considerably higher than normal (126). One of the primary contributors to the active period is the much warmer than normal North Atlantic basin sea surface temperature (SST) pattern featuring increased frequency of unusually warm SST of 30-31C (or warmer) which ignites major hurricanes.

Increasing attention is given to the recent uptick to large regions of oceanic warming outside of the tropical region. Marine heat waves are present across much of the middle/subtropical latitudes in both hemispheres causing a record warm ocean surface according to the Climate Change Institute at the University of Maine. Certainly, the evolution of an increasingly bold El Nino and recent near onset of positive phase Indian Ocean dipole has helped. The oceanic warming in the middle latitudes has caused warming aloft to increase high-pressure ridging to deliver hot weather to populated land masses for mid-summer in the northern hemisphere.     

Climate Impact Company is following 7 global marine heat waves (MHW) as the mid-point of 2023 approaches. The largest MHW stretches across the eastern North Atlantic basin and is a repeat of the 2022 episode although displaced slightly westward.